In-vehicle communication system, in-vehicle communication device, and transmission cycle calculation method

ABSTRACT

An in-vehicle communication device on a transmitting side of a message includes: a delay time measuring unit measuring a delay time from when transmission of a message is first attempted to when the transmission of the message is started; and an assigning unit assigning the delay time measured by the delay time measuring unit to the message. An in-vehicle communication device on a receiving side of a message includes: a reception point acquisition unit acquiring a point in time when a message from the in-vehicle communication device on the transmitting side is received; a delay time acquisition unit acquiring a delay time assigned to the received message; and a calculation unit calculating a transmission cycle of each message based on a point in time acquired by the reception point acquisition unit and a delay time acquired by the delay time acquisition unit for each of two received messages.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national stage of PCT/JP2020/021867 filedon Jun. 3, 2020, which claims priority of Japanese Patent ApplicationNo. JP 2019-115712 filed on Jun. 21, 2019, the contents of which areincorporated herein.

TECHNICAL FIELD

The present disclosure relates to an in-vehicle communication system andan in-vehicle communication device for transmitting and receiving amessage through a common communication line, and also to a transmissioncycle calculation method for calculating the transmission cycle of amessage transmitted periodically.

BACKGROUND

Conventionally, a plurality of devices, such as an ECU (ElectronicControl Unit), are mounted in a vehicle. The plurality of in-vehicledevices are connected to each other through a communication line,exchange information by transmitting and receiving messages, and realizevarious functions of the vehicle in cooperation with each other. Thecommunication standard of CAN (Controller Area Network) is widelyadopted for communication in the vehicle.

Japanese Patent Laid-Open Publication No. 2005-277896 proposes anin-vehicle network expansion device that can be expected to efficientlyarbitrate communication between communication lines when thecommunication lines of CAN arranged in a vehicle are divided into aplurality of systems. The in-vehicle network expansion device includes acircuit for arbitrating communication between the communication linesbased on the priority assigned to a message when a communicationcollision occurs between the communication lines.

SUMMARY

Devices such as an ECU mounted in a vehicle often periodically transmita message having predetermined information. By using this, a device onthe side of receiving a message can calculate a transmission cycle forthe received message and determine whether or not the received messageis correct by determining whether or not the calculated transmissioncycle is correct. However, message transmission by a plurality ofin-vehicle devices may occur at the same time to cause messagecollision, and transmission of a low-priority message may be delayed dueto arbitration processing. When the message transmission is delayed dueto the arbitration processing, it is difficult for the device thatreceives the message to calculate the transmission cycle. This may lowerthe accuracy of determination regarding whether or not the message iscorrect based on the transmission cycle.

The present disclosure has been made in view of such circumstances, andan object thereof is to provide an in-vehicle communication system, anin-vehicle communication device, and a transmission cycle calculationmethod capable of accurately calculating the transmission cycle of amessage.

An in-vehicle communication system according to this aspect is anin-vehicle communication system in which a plurality of in-vehiclecommunication devices connected to a common communication line transmitand receive messages through the communication line. An in-vehiclecommunication device on a transmitting side of a message includes: adelay time measuring unit that measures a delay time from a point intime when transmission of a message to be transmitted is first attemptedto a point in time when the transmission of the message is started; andan assigning unit that assigns the delay time measured by the delay timemeasuring unit to the message. An in-vehicle communication device on areceiving side of a message includes: a reception point acquisition unitthat acquires a point in time when a message from the in-vehiclecommunication device on the transmitting side is received; a delay timeacquisition unit that acquires a delay time assigned to the receivedmessage; and a calculation unit that calculates a transmission cycle ofeach message based on a point in time acquired by the reception pointacquisition unit and a delay time acquired by the delay time acquisitionunit for each of two received messages.

Not only can the present application be realized as an in-vehiclecommunication device including such characteristic processing units, butalso the present application can be realized as a communication methodincluding such characteristic processes as steps or can be realized as acomputer program causing a computer to execute such steps. The presentapplication can be realized as a semiconductor integrated circuit thatrealizes some or all of these devices, or can be realized as anotherdevice or system including these devices.

Advantageous Effects

According to the above, it can be expected that the transmission cycleof a message is accurately calculated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the configuration of an in-vehiclecommunication system according to the present embodiment.

FIG. 2 is a block diagram showing the configuration of an ECU accordingto the present embodiment.

FIG. 3 is a schematic diagram for explaining the configuration of amessage transmitted from an ECU in the in-vehicle communication systemaccording to the present embodiment.

FIG. 4 is a flowchart showing the procedure of a message transmissionprocess performed by a CAN controller according to the presentembodiment.

FIG. 5 is a schematic diagram for explaining a transmission cyclecalculation method according to the present embodiment.

FIG. 6 is a schematic diagram for explaining a transmission cyclecalculation method according to the present embodiment.

FIG. 7 is a flowchart showing the procedure of a transmission cyclecalculation process performed by the CAN controller according to thepresent embodiment.

FIG. 8 is a schematic diagram for explaining a method of a verificationexperiment of the transmission cycle calculation process according tothe present embodiment.

FIG. 9 is a graph showing the results of the verification experiment ofthe transmission cycle calculation process according to the presentembodiment.

FIG. 10 is a block diagram showing the configuration of an in-vehiclecommunication system according to a second embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

First, embodiments of the present disclosure will be listed anddescribed. At least some of the embodiments described below may bearbitrarily combined.

(1) An in-vehicle communication system according to this aspect is anin-vehicle communication system in which a plurality of in-vehiclecommunication devices connected to a common communication line transmitand receive messages through the communication line. An in-vehiclecommunication device on a transmitting side of a message includes: adelay time measuring unit that measures a delay time from a point intime when transmission of a message to be transmitted is first attemptedto a point in time when the transmission of the message is started; andan assigning unit that assigns the delay time measured by the delay timemeasuring unit to the message. An in-vehicle communication device on areceiving side of a message includes: a reception point acquisition unitthat acquires a point in time when a message from the in-vehiclecommunication device on the transmitting side is received; a delay timeacquisition unit that acquires a delay time assigned to the receivedmessage; and a calculation unit that calculates a transmission cycle ofeach message based on a point in time acquired by the reception pointacquisition unit and a delay time acquired by the delay time acquisitionunit for each of two received messages.

According to this aspect, a delay time from the point in time when thetransmission of a message is first attempted to the point in time whenthe transmission of the message is actually started is assigned to themessage by the in-vehicle communication device on the transmitting side.The message transmitted from the in-vehicle communication device on thetransmitting side is received by the in-vehicle communication device onthe receiving side connected to the common communication line. Thein-vehicle communication device on the receiving side acquires thereception point in time of the received message, and acquires the delaytime assigned to the received message. The in-vehicle communicationdevice on the receiving side acquires the reception point in time andthe delay time for each of the two messages received before and after inchronological order, and calculates the transmission cycle of themessage based on the acquired information. Since the in-vehiclecommunication device on the transmitting side transmits a message with adelay time assigned thereto and the in-vehicle communication device onthe receiving side acquires the delay time from the message andcalculates the transmission cycle, the in-vehicle communication deviceon the receiving side can calculate the transmission cycle of themessage in consideration of the delay of message transmission due toarbitration processing or the like in the in-vehicle communicationdevice on the transmitting side. Therefore, the in-vehicle communicationdevice on the receiving side can accurately calculate the transmissioncycle of the message.

(2) It is preferable that the calculation unit calculates, as thetransmission cycle, a time difference between a point in time that goesback by a delay time from a reception point in time of a messagereceived earlier and a point in time that goes back by the delay timefrom a reception point in time of a message received later.

According to this aspect, the point in time that goes back from thereception time of the message by the delay time is a point in time whenthe transmission of the message is first attempted. Therefore, thein-vehicle communication device on the receiving side calculates a timedifference between the point in time that goes back by the delay timefrom the reception point in time of the message received earlier and thepoint in time that goes back by the delay time from the reception pointin time of the message received later, and sets the time difference as atransmission cycle of the message. Since the in-vehicle communicationdevice on the receiving side can calculate the transmission cycle of themessage based on the point in time when the in-vehicle communicationdevice on the transmitting side first attempts to transmit the message,it is possible to accurately calculate the transmission cycle of themessage.

(3) It is preferable that the in-vehicle communication device on thereceiving side includes a periodic message determination unit thatdetermines whether the received message is a periodically transmittedmessage or an aperiodically transmitted message based on thetransmission cycle calculated by the calculation unit.

According to this aspect, based on the calculated transmission cycle ofthe message, the in-vehicle communication device on the receiving sidedetermines whether the received message has been transmittedperiodically or transmitted aperiodically. For example, each time amessage is received, the in-vehicle communication device on thereceiving side calculates a time difference in transmission point intime from the message received previously. When the calculated timedifference falls within a margin of error with respect to the previouslycalculated transmission cycle, it can be determined that the receivedmessage is transmitted periodically. On the other hand, when thecalculated time difference is a different value exceeding the margin oferror with respect to the transmission cycle, the in-vehiclecommunication device on the receiving side can determine that thereceived message is transmitted aperiodically. The message determined tobe aperiodic may be, for example, a message transmitted by event drivingor an invalid message by an invalid device.

(4) It is preferable that plurality of in-vehicle communication devicesinclude an in-vehicle communication device that has the delay timemeasuring unit and the assigning unit and an in-vehicle communicationdevice that does not have the delay time measuring unit and theassigning unit.

According to this aspect, the plurality of in-vehicle communicationdevices connected to the common communication line include an in-vehiclecommunication device that transmits a message with a delay time assignedthereto and an in-vehicle communication device that transmits a messagewithout assigning a delay time. That is, in the in-vehicle communicationsystem, a message with a delay time and a message without a delay timecan be mixed. A function of assigning a delay time to an in-vehiclecommunication device, which is required to accurately determine thetransmission cycle of a message, may be added to the in-vehiclecommunication system having a conventional configuration that does notassign a delay time. Therefore, it is possible to easily introduce theconfiguration of the in-vehicle communication system of this aspect intoa conventional vehicle.

(5) It is preferable that identification information for identifying themessage is added to the message and that the in-vehicle communicationdevice on the receiving side includes an assignment determination unitthat determines whether or not a delay time is assigned to the messagebased on identification information added to the received message.

According to this aspect, identification information for identifying themessage is added to the message transmitted and received by thein-vehicle communication device. The message identification informationcan be, for example, CAN-ID in the CAN communication standard. However,the communication of this aspect is not limited to the communicationstandard of CAN, and various communication standards such as FlexRay orEthernet (registered trademark) can be adopted. The in-vehiclecommunication device on the receiving side determines whether or not adelay time is assigned to the message based on the identificationinformation of the received message. As a result, even when a messagewith a delay time and a message without a delay time are mixed, thein-vehicle communication device on the receiving side can calculate thetransmission cycle of the message.

(6) An in-vehicle communication device according to this aspect is anin-vehicle communication device that is connected to a commoncommunication line together with other in-vehicle communication devicesand transmits and receives a message through the communication line. Thein-vehicle communication device includes: a reception unit that receivesa message with a delay time from a point in time when transmission of amessage to be transmitted is first attempted to a point in time when thetransmission of the message is started; a reception point acquisitionunit that acquires a point in time when the reception unit receives themessage; a delay time acquisition unit that acquires a delay timeassigned to the received message; and a calculation unit that calculatesa transmission cycle of each message based on a point in time acquiredby the reception point acquisition unit and a delay time acquired by thedelay time acquisition unit for each of two received messages.

According to this aspect, as in the aspect (1), it is possible toaccurately calculate the transmission cycle of the message.

(7) A transmission cycle calculation method according to this aspect isa transmission cycle calculation method for calculating a transmissioncycle of each message transmitted and received through a commoncommunication line by a plurality of in-vehicle communication devicesconnected to the common communication line. The transmission cyclecalculation method includes: measuring a delay time from a point in timewhen transmission of a message to be transmitted is first attempted to apoint in time when the transmission of the message is started andassigning the measured delay time to the message by an in-vehiclecommunication device on a transmitting side of a message; and acquiringa point in time when a message from the in-vehicle communication deviceon the transmitting side is received, acquiring a delay time assigned tothe received message, and calculating a transmission cycle of eachmessage based on a point in time and a delay time acquired for each oftwo received messages by an in-vehicle communication device on areceiving side of a message.

According to this aspect, as in the aspect (1), it is possible toaccurately calculate the transmission cycle of the message.

Specific examples of in-vehicle communication systems according toembodiments of the present disclosure will be described below withreference to the diagrams. In addition, the present disclosure is notlimited to these examples but is defined by the claims, and is intendedto include all modifications within the meaning and scope equivalent tothe claims.

System Configuration

FIG. 1 is a block diagram showing the configuration of an in-vehiclecommunication system according to the present embodiment. The in-vehiclecommunication system according to the present embodiment is configuredto include a plurality of ECUs 2 mounted in a vehicle 1. Each of theplurality of ECUs 2 is connected to a communication line 4 arranged inthe vehicle 1, and can transmit and receive a message through thecommunication line 4. In addition, in the present embodiment, theplurality of ECUs 2 transmit and receive messages according to the CANcommunication standard. The communication line 4 is called a CAN bus,and several to a dozen or more ECUs 2 can be connected to onecommunication line 4. A plurality of communication lines 4 may beprovided in the vehicle 1. In this case, a device such as a gateway thatrelays a message between the communication lines 4 is mounted in thevehicle. In addition, the number of ECUs 2 included in the in-vehiclecommunication system, the number of communication lines 4, theconnection mode of each devices, the network configuration, and the likeare not limited to those shown in the diagrams.

As the ECU 2, for example, various ECUs such as an ECU that controls theoperation of the engine of the vehicle 1, an ECU that controlslocking/unlocking of the door, an ECU that controls ON/OFF of the light,an ECU that controls the operation of the airbag, and an ECU thatcontrols the operation of an ABS (Antilock Brake System). In addition,in the present embodiment, the ECU 2 is mentioned as an in-vehiclecommunication device for transmitting and receiving a message throughthe communication line 4, but the in-vehicle communication device is notlimited thereto.

In a message according to the CAN communication standard, identificationinformation called CANID is stored in the head area of the messagecalled an arbitration field. The CANID is information indicating thetype of data included in the message and the priority of the message.The smaller the value of CANID, the higher the priority of the message.When a plurality of ECUs 2 attempt to transmit messages to thecommunication line 4 at the same time, in the CAN communicationstandard, arbitration processing based on the CANID value stored in thearbitration field of the message is performed by each ECU 2. As a resultof the arbitration processing, one message with the highest priority isallowed to be transmitted, and the other messages need to wait fortransmission. The CANID is a value determined by the designer at thedesign stage or the like of the vehicle 1, the in-vehicle communicationsystem, or the ECU 2.

In the in-vehicle communication system according to the presentembodiment, the ECU 2 adds the information of delay time caused byarbitration processing to the message and transmits the message. The ECU2 that has received the message can calculate the time (point in time)at which the ECU 2 as a transmission source has attempted to transmitthe message first, that is, transmission time (transmission point intime) at which the ECU 2 as a transmission source could transmit themessage if there is no delay due to arbitration processing, based on themessage reception time (reception point in time) and the delay timeassigned to the message.

In addition, in the present embodiment, each ECU 2 repeatedly transmitsa message at a predetermined cycle. The transmission cycle is set inadvance, for example, for each ECU 2 or for each message type (that is,for each CANID). The ECU 2 that has received the message calculates atime difference from the previous message transmission time to thecurrent message transmission time based on the reception time and delaytime of the received message and the reception time and delay time ofthe previous received message having the same CANID as the receivedmessage. The calculation of the time difference corresponds to theprocess of calculating the transmission cycle of the message.

The ECU 2 according to the present embodiment calculates thetransmission cycle of the message each time a message is received. TheECU 2 compares the calculation result of the current transmission cyclewith the calculation result of the previous transmission cycle, anddetermines that the current received message is not the expectedperiodic message when the current transmission cycle is significantlydifferent from the previous transmission cycle. In the presentembodiment, the message determined by the ECU 2 to be not a periodicmessage is regarded as an invalid message and discarded. Here, theaperiodic message may be processed as a valid message, such as an eventmessage.

FIG. 2 is a block diagram showing the configuration of the ECU 2according to the present embodiment. The ECU 2 according to the presentembodiment is configured to include a processing unit (processor) 21, astorage unit (storage) 22, an input/output unit (I/O) 23, and a CANcontroller 24. The processing unit 21 reads and executes a program 22 astored in the storage unit 22 to perform various processes such ascontrol processing of the vehicle 1. When it is necessary to transmit amessage to another ECU 2 in control processing or the like, theprocessing unit 21 sends a message to be transmitted to the CANcontroller 24 and instructs the CAN controller 24 to transmit themessage. In addition, in the present embodiment, the processing unit 21performs a process of calculating the transmission cycle of the receivedmessage.

The storage unit 22 is configured by using a non-volatile memoryelement, such as a flash memory or an EEPROM (Electrically ErasableProgrammable Read Only Memory). The storage unit 22 stores variousprograms executed by the processing unit 21 and various kinds of datarequired for the processing of the processing unit 21. In the presentembodiment, the storage unit 22 stores the program 22 a executed by theprocessing unit 21.

The program 22 a may be written into the storage unit 22 at themanufacturing stage of the ECU 2, for example. For example, the program22 a distributed by a remote server device or the like may be acquiredby the ECU 2 through communication. For example, the ECU 2 may read outthe program 22 a recorded on a recording medium, such as a memory cardor an optical disk, and store the program 22 a in the storage unit 22.For example, the program 22 a recorded on a recording medium may be readout by a writing device and written into the storage unit 22 of the ECU2. The program 22 a may be provided in the form of distribution througha network, or may be provided in a form recorded on a recording medium.

Devices, such as a sensor 5 a and an actuator 5 b, are connected to theinput/output unit 23 through a signal line or the like. The input/outputunit 23 samples and acquires a signal input from an input device, suchas the sensor 5 a, and transmits the acquired information to theprocessing unit 21. In addition, when a control command for a controltarget device, such as the actuator 5 b, is given from the processingunit 21, the input/output unit 23 outputs a control signal correspondingto the control command. The ECU 2 does not need to perform both inputand output, and may be configured to perform only input or only output,and may be configured to perform neither input nor output.

The CAN controller 24 performs processing relevant to the transmissionand reception of a message through the communication line 4. The CANcontroller 24 can be configured as, for example, one IC (IntegratedCircuit). The CAN controller 24 is connected to the communication line 4arranged in the vehicle 1, and transmits and receives a message to andfrom another ECU 2 through the communication line 4 according to the CANcommunication standard. The CAN controller 24 transmits a message toanother ECU 2 by converting a transmission message given from theprocessing unit 21 into an electrical signal corresponding to the CANcommunication standard and outputting the electrical signal to thecommunication line 4. The CAN controller 24 receives a message fromanother ECU 2 by sampling and acquiring the potential of thecommunication line 4, and sends the received message to the processingunit 21.

In addition, the CAN controller 24 according to the present embodimentincludes a transmission processing unit 24 a, a delay time measuringunit 24 b, a delay time assigning unit 24 c, a reception processing unit24 d, a reception time acquisition unit 24 e, and a delay timeacquisition unit 24 f When a message to be transmitted and atransmission instruction are given from the processing unit 21, thetransmission processing unit 24 a performs a process of transmitting themessage to another ECU 2 by outputting the message to the communicationline 4. In addition, the transmission processing unit 24 a performsarbitration processing when the message transmissions of other ECUs 2are performed at the same time. The transmission processing unit 24 atransmits a message when the transmission right is acquired by thearbitration processing.

The delay time measuring unit 24 b performs a process of measuring thetime during which the message transmission is delayed because thetransmission right cannot be acquired by the arbitration processing. Thedelay time measuring unit 24 b measures the delay time by using acounter. For example, the delay time measuring unit 24 b starts the timemeasurement of the counter when a message to be transmitted and atransmission instruction are given from the processing unit 21.Thereafter, the delay time measuring unit 24 b acquires the value of thecounter at the point in time when the transmission right is acquired bythe arbitration processing, and sets the value as the delay time. Forexample, when the value of the counter is 100 and the clock period foroperating the counter is 1 μsec, the actual delay time is 100 μsec. Inthe present embodiment, it is assumed that the value of the clock periodof the counter is known to the plurality of ECUs 2, and the value ofthis counter is treated as the delay time.

The delay time assigning unit 24 c performs a process of assigning thedelay time (counter value corresponding to the delay time) measured bythe delay time measuring unit 24 b to the transmitted message. The delaytime assigning unit 24 c stores the delay time in a part of the datafield of the message according to the communication standard of CAN, forexample.

The reception processing unit 24 d performs a process of receiving amessage transmitted from another ECU 2. The reception processing unit 24d receives a message by repeatedly sampling the potential of thecommunication line 4, and sends the received message to the processingunit 21.

The reception time acquisition unit 24 e performs a process of acquiringthe time when the reception processing unit 24 d receives a message fromanother ECU 2. In the present embodiment, the CAN controller 24 has atimer function for measuring the current time. The time measured by theCAN controller 24 may be an absolute time shared with other devices, ormay be a relative time used only by its own device. For example, thetimer function is realized by a counter, and by operating the counter atthe same time as the CAN controller 24 is started, the relative timefrom the start can be measured by the counter. The reception timeacquisition unit 24 e acquires the reception time of the message byacquiring the value of the timer function counter at the timing when themessage is received.

The delay time acquisition unit 24 f performs a process of acquiringinformation of the delay time assigned to the received message. In thepresent embodiment, the delay time information is stored in a part ofthe data field of the message. The delay time acquisition unit 24 fextracts and acquires the delay time information from a predeterminedlocation in the data field of the received message.

The CAN controller 24 transmits information, such as the content of themessage received by the reception processing unit 24 d, the receptiontime acquired by the reception time acquisition unit 24 e, and the delaytime acquired by the delay time acquisition unit 24 f, to the processingunit 21.

In the present embodiment, a transmission cycle calculation unit 21 a isprovided in the processing unit 21. The transmission cycle calculationunit 21 a is a software-like functional block realized by executing theprogram 22 a stored in the storage unit 22 with the processing unit 21.However, the transmission cycle calculation unit 21 a may be realized asa hardware-like functional block.

As described above, each time a message is received, the CAN controller24 transmits information, such as the content of the message, thereception time, and the delay time, to the processing unit 21. Based onthe information transmitted from the CAN controller 24, the transmissioncycle calculation unit 21 a of the processing unit 21 performs a processof calculating the transmission cycle of the message by calculating thetime difference between the received message and the previously receivedmessage. Therefore, the transmission cycle calculation unit 21 a storesthe information of the reception time and the delay time (or may beinformation of the transmission time of the message calculated from thereception time and the delay time) of the previously received message.The transmission cycle calculation unit 21 a calculates the transmissioncycle of the message based on the reception time and delay time of theprevious received message and the reception time and delay time of thecurrent received message.

For example, it is assumed that a certain ECU α periodically transmits amessage Mα and the transmission cycle of the message is Tα. That is, inthe ECU α, a transmission message and a transmission instruction aregiven from the processing unit 21 to the CAN controller 24 in a cycleTα. When an ECU β receives the message Ma transmitted from the ECU α,the sequence of the reception time of messages Mα0, Mα1, . . . , Mαnconsecutively received by the ECU β is tβ={tβ0, tβ1, . . . , tβn}. Atthis time, the sequence of delay time corresponding to each receptiontime is d={d0, d1, . . . , dn}.

In this case, with respect to the message Mα0 received by the ECU β atthe reception time tβ0, the time (message generation time) tα0 at whicha transmission instruction is given by the ECU α can be calculated byusing the following Equation (1).

tα0=tβ0−d0  (1)

Therefore, the transmission interval Tβ between the two consecutivemessages Mα0 and Mα1 can be calculated by using the following Equation(2).

Tβ=(tβ1−d1)−(tβ0−d0)  (2)

The transmission interval Tβ calculated by this Equation (2) correspondsto the transmission cycle Tα of the message M by the ECU α. However,since there are errors in the clock signals of the ECU α and the ECU β,there may be differences due to these errors in Tα and Tβ. That is,Tβ=Tα. In addition, the CAN controller 24 may include the transmissioncycle calculation unit 21 a. In this case, the CAN controller 24transmits the calculation result of the transmission cycle to theprocessing unit 21.

The processing unit 21 can determine whether or not the received messageis correct based on the transmission cycle calculated by thetransmission cycle calculation unit 21 a. In addition, in the presentembodiment, the processing unit 21 calculates the transmission cycle ofthe received message, but the CAN controller 24 may calculate thetransmission cycle, and the CAN controller 24 may transmit thecalculation result to the processing unit 21. In this case, the CANcontroller 24 may determine whether or not the received message iscorrect based on the calculated transmission cycle.

Transmission Cycle Calculation Method

FIG. 3 is a schematic diagram for explaining the configuration of amessage transmitted from the ECU 2 in the in-vehicle communicationsystem according to the present embodiment. The message according to theCAN communication standard includes an arbitration field, a controlfield, a data field, a CRC (Cyclic Redundancy Check) field, and an ACKfield. In the message according to the present embodiment, the CANID isstored in the arbitration field, and the delay time information isstored in a part of the data field.

According to the CAN communication standard, the size of the data fieldof a message is up to 8 bytes. In 8 bytes, the size of the area forstoring the delay time can be, for example, 2 bytes to 4 bytes. The sizeof the delay time is determined in advance at the design stage of thein-vehicle communication system or the like, for example, based on themaximum delay time. Assuming that the period of the clock signal foroperating the counter for measuring the delay time is, for example, 2μsec, the maximum delay time of 2 bytes is about 130 msec, the maximumdelay time of 3 bytes is about 33 seconds, and the maximum delay time of4 bytes is about 67 seconds.

The CAN controller 24 starts the transmission of the message byoutputting the message given from the processing unit 21 to thecommunication line 4 in order from the MSB (Most Significant Bit) side,that is, the arbitration field side. Upon starting the transmission ofthe message, the CAN controller 24 starts measuring the delay time bythe counter. The arbitration processing is performed from the start ofmessage transmission to the completion of transmission of thearbitration field, and the result of the arbitration processing, thatis, whether or not there is a message transmission right, is determinedat the point in time when the transmission of the final bit of thearbitration field is completed. When the acquisition of the transmissionright is determined by the arbitration processing, the CAN controller 24acquires the delay time measured by the counter and stores the acquireddelay time in a predetermined location of the data field. Thereafter,the CAN controller 24 transmits the control field, the data field, theCRC field, and the ACK field in this order, and completes the messagetransmission.

FIG. 4 is a flowchart showing the procedure of a message transmissionprocess performed by the CAN controller 24 according to the presentembodiment. The transmission processing unit 24 a of the CAN controller24 according to the present embodiment determines whether or not atransmission instruction has been given from the processing unit 21together with a message to be transmitted (step S1). If no transmissioninstruction is given (S1: NO), the transmission processing unit 24 awaits until the transmission instruction is given. If a transmissioninstruction is given (S1: YES), the delay time measuring unit 24 b ofthe CAN controller 24 starts counting the delay time by the counter(step S2).

The transmission processing unit 24 a starts transmission from thebeginning of the transmission message, and performs arbitration fieldtransmission processing first (step S3). At this time, the transmissionprocessing unit 24 a performs arbitration processing between the ECU 2and another ECU 2, and the presence or absence of the transmission rightis determined by transmitting the final bit of the arbitration field.The transmission processing unit 24 a determines whether or not it ispossible to transmit its own message based on the result of thearbitration processing (step S4). If the message cannot be transmitted(S4: NO), the transmission processing unit 24 a waits until the messagetransmission by another ECU 2 ends (step S5), and the process returns tostep S3 to attempt the message transmission again.

If the message can be transmitted (S4: YES), the delay time measuringunit 24 b acquires the delay time counted by the counter (step S6). Thedelay time assigning unit 24 c of the CAN controller 24 assigns thedelay time acquired in step S6 to a predetermined location in the datafield of the transmitted message (step S7). The transmission processingunit 24 a performs transmission processing for the control field andsubsequent fields of the transmission message (step S8), and ends themessage transmission process.

FIGS. 5 and 6 are schematic diagrams for explaining a transmission cyclecalculation method according to the present embodiment. FIG. 5 shows arelationship between time (point in time) and time for one message. Inthe example shown in FIG. 5, the point in time when the CAN controller24 first attempts to transmit a message according to a transmissioninstruction from the processing unit 21 is the transmission start timet0. In this example, the transmission of the message is made to stand bydue to the message transmission of another ECU 2, and the transmissionof the message is attempted again at the subsequent time t1. Thetransmission right of the message is determined at time t2 when thefinal bit of the arbitration field is transmitted, and the delay time Dat this point in time is assigned to a predetermined location in thedata field of the message. The CAN controller 24 transmits the remainingpart of the message and completes the transmission of the message attime t3. Thereafter, at time t4 at which the transmission cycle T of themessage has passed from the message transmission start time t0, the CANcontroller 24 attempts to transmit the next message.

The CAN controller 24 of the ECU 2 that receives the message sets thetime t2 at which the transmission of the message is determined by thearbitration processing as the reception time of the message. The CANcontroller 24 completes the reception of the message at the subsequenttime t3, and acquires the delay time D from a predetermined location inthe data field of the received message. The CAN controller 24 transmitsinformation of the message reception time and the delay time to theprocessing unit 21. The processing unit 21 can calculate the time t0that goes back from the message reception time t2 by the delay time D asthe message transmission time t0. Each time the CAN controller 24receives a message, the processing unit 21 calculates the messagetransmission time in the same manner and calculates the time differencebetween the transmission times of two consecutive received messages inchronological order, thereby being able to calculate the transmissioncycle T of the message.

In addition, for the delay time D assigned to the message by the CANcontroller 24 of the ECU 2 on the transmitting side, the length of themessage to be transmitted may be calculated in advance, and the timeuntil the time t3 when the transmission of the message is completed,that is, the time corresponding to (t3−t0), may be set as the delay timeD. In this case, the ECU 2 on the receiving side sets the point in timewhen the message reception is completed as a message reception time.

FIG. 6 shows examples of reception time and delay time for four messagesM0 to M3. In addition, the reception time, the delay time, and the likein this diagram are shown by using counter values measured by a timerfunction counter provided in the CAN controller 24 of the ECU 2 thatreceives the message. For example, the message M0 is received at thereception time 1100, and 100 is given as a delay time. Similarly, themessage M1 is received at the reception time 2100, and 100 is given as adelay time. The message M2 is received at the reception time 3210, and210 is given as a delay time. The message M3 is received at thereception time 4175, and 175 is given as a delay time.

The ECU 2 that has received the message can calculate the time that goesback from the message reception time by the delay time as a transmissiontime. In this example, the transmission time of the message M0 is 1000,the transmission time of the message M1 is 2000, the transmission timeof the message M2 is 3000, and the transmission time of the message M3is 4000. The ECU 2 calculates the time difference between thetransmission times of two consecutive messages in chronological order.In this example, the time difference between the transmission times ofthe messages M0 and M1 is 1000, the time difference between thetransmission times of the messages M1 and M2 is 1000, and the timedifference between the transmission times of the messages M2 and M3 is1000. Therefore, the ECU 2 can determine that the transmission cycle ofthe message is 1000.

FIG. 7 is a flowchart showing the procedure of a transmission cyclecalculation process performed by the ECU 2 according to the presentembodiment. The reception processing unit 24 d of the CAN controller 24of the ECU 2 according to the present embodiment determines whether ornot another ECU 2 has transmitted a message to the communication line 4(step S21). If no message is transmitted (S21: NO), the receptionprocessing unit 24 d waits until another ECU 2 transmits a message.

When a message is transmitted from another ECU 2 (S21: YES), thereception time acquisition unit 24 e of the CAN controller 24 acquiresthe reception time of the message based on the timer function of the CANcontroller 24 (step S22). At this time, the reception time acquisitionunit 24 e acquires the point in time when the reception of the messageup to the arbitration field is completed as a reception time.Thereafter, the delay time acquisition unit 24 f of the CAN controller24 acquires the delay time assigned to a predetermined location in thedata field of the received message (step S23). The information of thereception time and the delay time acquired by the CAN controller 24 isgiven to the processing unit 21. The transmission cycle calculation unit21 a of the processing unit 21 reads out the information of thereception time and the delay time stored for the previously receivedmessage (step S24). The transmission cycle calculation unit 21 acalculates the transmission cycle of the message based on the receptiontime and the delay time of the previous received message and thereception time and the delay time of the current received message (stepS25).

The processing unit 21 determines whether or not the transmission cyclecalculated in step S25 is a correct transmission cycle (step S26). Forexample, the processing unit 21 has information, such as a table inwhich a valid transmission cycle is set in advance for the CANID of amessage. By determining whether or not the calculated transmission cyclematches the valid transmission cycle stored in the table or the like ordetermining whether or not the difference between the calculatedtransmission cycle and the valid transmission cycle is within athreshold value, the processing unit 21 can determine whether or not thecalculated transmission cycle is valid. In addition, for example, bycomparing the previously calculated transmission cycle with thetransmission cycle calculated this time and determining whether or notthe difference between the two transmission cycles is within a thresholdvalue, the processing unit 21 can determine whether or not thetransmission cycle is valid. The determination regarding whether or notthe transmission cycle is correct may be performed by using any method.

If the processing unit 21 determines that the transmission cycle of thereceived message is a correct transmission cycle (S26: YES), theprocessing unit 21 performs reception processing of the message (stepS27), and performs various processes according to the content of thereceived message. In addition, the processing unit 21 stores informationof the reception time and the delay time for the message received thistime (step S28), and ends the process. The reception time and the delaytime are stored by using a storage area such as a register inside thestorage unit 22 or the processing unit 21.

In addition, if the processing unit 21 determines that the transmissioncycle of the received message is not a correct transmission cycle (S26:NO), the processing unit 21 performs processing for discarding themessage (step S29), and ends the process. For example, the processingunit 21 does not perform processing using the received message, therebydiscarding the message. In addition, in the case of a configuration inwhich the CAN controller 24 calculates and determines the transmissioncycle, the CAN controller 24 may output an error frame to thecommunication line 4 before the reception of the message determined tohave an incorrect transmission cycle is completed, so that it isprevented that the message is received by another ECU 2.

In addition, in this flowchart, a message determined to have anincorrect transmission cycle is treated as an invalid message, but thepresent disclosure is not limited thereto. For example, a messagedetermined to have an incorrect transmission cycle may be treated as avalid aperiodic message, such as an event message.

Verification Experiment

FIG. 8 is a schematic diagram for explaining a method of a verificationexperiment of the transmission cycle calculation process according tothe present embodiment. A PC (Personal Computer) 101, a verificationboard 102, a load generating device 103, and a measurement device 104are used in the verification experiment of the transmission cyclecalculation process according to the present embodiment. The PC 101 is ageneral-purpose computer, and software for controlling the operation ofthe load generating device 103, software for acquiring the measurementresult of the measurement device 104, and the like are installed. Theverification board 102 is an FPGA (Field Programmable Gate Array) inwhich the functions of the ECU 2 according to the present embodiment areimplemented. In this verification, “DE2-115” mounted with the FPGA ofALTERA is used as the verification board 102. The verification board 102is connected to the communication line 4 corresponding to the CAN bus,and transmits a message to be verified, that is, a message with a delaytime at a predetermined cycle.

The load generating device 103 is a device for transmitting a message toobstruct a verification target message transmitted from the verificationboard 102 to the communication line 4. The message to obstruct averification target message corresponds to a message transmitted fromanother ECU 2 to the communication line 4, and is a message that delaysthe verification target message by arbitration processing. The loadgenerating device 103 is connected to the PC 101, and the frequency ofmessage transmission to the communication line 4 and the like arecontrolled by the PC 101. In this verification, PEAK System's “PCAN-USB”is used as the load generating device 103.

The measurement device 104 is a device that receives a messagetransmitted to the communication line 4 and transmits information, suchas the content of the received message and the reception time, to the PC101. In this verification, Vector's “VN1630A” is used as the measurementdevice 104, and the company's software “CANoe” is operated on the PC 101to obtain the verification result. The verification board 102 in thisverification corresponds to the transmitting side ECU 2 in thein-vehicle communication system according to the present embodiment, andthe measurement device 104 and the PC 101 correspond to the ECU 2 on thereceiving side. The transmission cycle calculation of the ECU 2according to the present embodiment is performed by the PC 101 based onthe information transmitted from the measurement device 104.

FIG. 9 is a graph showing the results of the verification experiment ofthe transmission cycle calculation process according to the presentembodiment. In this verification, periodic message transmission from theverification board 102 was performed 1000 times, and the message wasreceived and the transmission cycle was calculated by the PC 101. Inaddition, the load generating device 103 transmits a load message sothat the occupancy rate of the communication line 4 becomes 50%. Thetransmission cycle was calculated by using two methods of a transmissioncycle calculation method according to the above-described embodiment inwhich the delay time assigned to the message is used and a conventionalmethod in which the transmission cycle is calculated only by the timedifference between reception times without using the delay time. In thegraph shown in FIG. 9, the results of the verification experiment areshown with the reception order of received messages on the horizontalaxis and the transmission cycle [seconds] calculated based on thereceived messages on the vertical axis. The calculation result of thetransmission cycle by the transmission cycle calculation methodaccording to the present embodiment is shown by black circles on thegraph, and the calculation result by the conventional method is shown bywhite circles on the graph.

According to the results of the verification experiment shown in thediagram, the transmission cycle calculated by this method isconcentrated on either 0.9987 or 0.9988, but the transmission cyclecalculated by the conventional method varies widely between 0.9982 and0.9992. In addition, the reason why the result of this method is dividedinto two transmission cycles is due to the variation in the transmissiontiming of the message by the verification board 102 used in theverification experiment. The verification board 102 transmits a messageat two timings when the transmission cycle is 0.9987 or 0.9988.Therefore, the message transmission cycle calculated by this method haslittle variation in the calculation result, and the transmission cycleof the transmission source is accurately calculated.

Summary

In the in-vehicle communication system according to the presentembodiment having the above-described configuration, a delay time fromthe point in time when the ECU 2 on the transmitting side first attemptsto transmit the message to the point in time when the message isactually transmitted is assigned to the message. The message transmittedfrom the ECU 2 on the transmitting side is received by the ECU 2 on thereceiving side connected to the common communication line 4. The ECU 2on the receiving side acquires the reception time of the receivedmessage, and acquires the delay time assigned to the received message.The ECU 2 on the receiving side acquires the reception time and thedelay time for each of the two messages received before and after inchronological order, and calculates the transmission cycle of themessage based on the acquired information. Since the ECU 2 on thetransmitting side transmits a message with a delay time assigned theretoand the ECU 2 on the receiving side acquires the delay time from themessage and calculates the transmission cycle, the ECU 2 on thereceiving side can calculate the transmission cycle of the message inconsideration of the delay of message transmission due to arbitrationprocessing or the like in the ECU 2 on the transmitting side. Therefore,the ECU 2 on the receiving side can accurately calculate thetransmission cycle of the message.

In addition, in the present embodiment, the time that goes back from thereception time of the message by the delay time is the time when thetransmission of the message is first attempted, that is, thetransmission time of the message. Therefore, the ECU 2 on the receivingside calculates a time difference between the time that goes back by thedelay time from the reception time of the message received earlier andthe time that goes back by the delay time from the reception time of themessage received later, and sets the time difference as a transmissioncycle of the message. Since the ECU 2 on the receiving side cancalculate the transmission cycle of the message based on the time whenthe ECU 2 on the transmitting side first attempts to transmit themessage, it is possible to accurately calculate the transmission cycleof the message.

In addition, in the present embodiment, based on the calculatedtransmission cycle of the message, the ECU 2 on the receiving sidedetermines whether the received message has been transmittedperiodically at a valid transmission cycle or transmitted aperiodicallyat an invalid transmission cycle. For example, each time a message isreceived, the ECU 2 on the receiving side calculates a time differencein transmission time from the message received previously. When thecalculated time difference falls within a predetermined range withrespect to the previously calculated transmission cycle, it can bedetermined that the received message is transmitted periodically. On theother hand, when the calculated time difference is a different valueexceeding the predetermined range with respect to the transmissioncycle, the ECU 2 on the receiving side can determine that the receivedmessage is transmitted aperiodically. The message determined to beaperiodic may be, for example, a message transmitted by event driving oran invalid message by an invalid device.

In addition, in the present embodiment, the ECU 2 is configured totransmit and receive a message according to the CAN communicationstandard, but the present disclosure is not limited thereto. Forexample, transmission and reception of a message according to the CAN-FD(CAN with Flexible Data rate) communication standard may be performed.In addition, the ECU 2 may be configured to transmit and receive amessage according to a communication standard different from the CAN. Inaddition, in the present embodiment, some or all of the processesperformed by the transmission processing unit 24 a to the transmissioncycle calculation unit 21 a provided in the CAN controller 24 may beperformed by the processing unit 21 of the ECU 2. In addition, some orall of the processes shown in the flowchart of FIG. 7 may not beperformed by the CAN controller 24, but may be performed by theprocessing unit 21. In addition, the CAN controller 24 is configured tostore the reception time and the delay time of the received message, butmay be configured to stores the transmission time of the messagecalculated based on the reception time and the delay time without beinglimited to the above.

Second Embodiment

FIG. 10 is a block diagram showing the configuration of an in-vehiclecommunication system according to a second embodiment. The in-vehiclecommunication system according to the second embodiment is a systemincluding an ECU 2A having a function of assigning a delay time to amessage, an ECU 2C having a function of calculating a transmission cyclebased on the delay time assigned to the message, and an ECU 2B havingneither of these functions.

The ECU 2A assigns a delay time to the message transmitted by itself byusing the above method. However, the ECU 2A does not perform processingfor calculating the transmission cycle for the reception of the message,but only receives the message according to the normal CAN communicationstandard. The ECU 2B does not perform the above-described processing,such as assigning the delay time and calculating the transmission cycle,and transmits and receives a message according to the normal CANcommunication standard. The ECU 2B may treat the message with a delaytime assigned thereto, which is transmitted from the ECU 2A, as amessage according to the normal CAN communication standard. The ECU 2Cperforms processing for calculating the transmission cycle using thedelay time assigned to the message by using the method described above.However, the ECU 2C does not perform processing for assigning a delaytime to the message transmitted by itself.

In the in-vehicle communication system according to the secondembodiment, a message with a delay time and a message without a delaytime are mixed. Therefore, each time a message is received, the ECU 2Cneeds to determine whether the message is a message with a delay time ora message without a delay time. The ECU 2C according to the secondembodiment stores in advance a table in which a CANID assigned to amessage and information indicating whether or not a delay time isassigned to the message are associated with each other. The ECU 2Cacquires the CANID of the received message and refers to the table todetermine whether or not a delay time is assigned to the message. TheECU 2C performs processing for calculating the transmission cycle forthe message to which the delay time is assigned.

In the in-vehicle communication system according to the secondembodiment having the above-described configuration, the plurality ofECUs 2 connected to the common communication line 4 include the ECU 2Athat transmits a message with a delay time assigned thereto and the ECUs2B and 2C that transmit a message without assigning a delay time. Thatis, in the in-vehicle communication system according to the secondembodiment, a message with a delay time and a message without a delaytime are mixed. Since a function of assigning a delay time only to theECU 2A, which is required to accurately determine the transmission cycleof a message, may be added to the in-vehicle communication system of CANhaving a conventional configuration for transmitting and receiving amessage without a delay time assigned thereto, it is possible to easilyintroduce a configuration for determining a transmission cycle using adelay time into a conventional in-vehicle communication system.

In addition, in the in-vehicle communication system according to thesecond embodiment, a CANID for identifying a message is assigned to themessages transmitted and received by the ECUs 2A to 2C. The ECU 2C thatreceives a message can determine whether or not a delay time is assignedto the message based on the CANID of the received message. As a result,even when a message with a delay time and a message without a delay timeare mixed, the ECU 2C on the receiving side can calculate thetransmission cycle of the message.

In addition, the in-vehicle communication system according to the secondembodiment has a configuration in which three types of ECUs 2A to 2C aremixed, but ECUs having other configurations may be further mixed. Forexample, an ECU having a function of transmitting a message with a delaytime assigned thereto and a function of calculating the transmissioncycle using the delay time assigned to the message may be further mixed.In addition, a plurality of ECUs similar to the ECUs 2A and 2C may beincluded in the in-vehicle communication system. In addition, the ECU 2Cis configured to determine whether or not a delay time is assigned tothe received message by referring to the table stored in advance, butthe present disclosure is not limited thereto. For example, informationsuch as a flag indicating the presence or absence of a delay time may beincluded in the message.

Each device in the in-vehicle communication system includes a computerconfigured to include a microprocessor, a ROM, a RAM, and the like. Anarithmetic processing unit, such as a microprocessor, may read acomputer program including a part or all of each step of a sequencediagram or a flowchart shown in FIGS. 4 and 7 from a storage unit, suchas a ROM or a RAM, and execute the computer program. Each of thecomputer programs of the plurality of devices can be installed from anexternal server device or the like. In addition, each of the computerprograms of the plurality of devices is distributed in a state of beingstored in a recording medium, such as a CD-ROM, a DVD-ROM, or asemiconductor memory.

It should be considered that the embodiments disclosed are examples inall points and not restrictive. The scope of the present disclosure isdefined by the claims rather than the meanings set forth above, and isintended to include all modifications within the scope and meaningequivalent to the claims.

1. An in-vehicle communication system in which a plurality of in-vehiclecommunication devices connected to a common communication line transmitand receive messages through the communication line, wherein anin-vehicle communication device on a transmitting side of a messageincludes: a delay time measuring unit that measures a delay time from apoint in time when transmission of a message to be transmitted is firstattempted to a point in time when the transmission of the message isstarted; and an assigning unit that assigns the delay time measured bythe delay time measuring unit to the message, and an in-vehiclecommunication device on a receiving side of a message includes: areception point acquisition unit that acquires a point in time when amessage from the in-vehicle communication device on the transmittingside is received; a delay time acquisition unit that acquires a delaytime assigned to the received message; and a calculation unit thatcalculates a transmission cycle of each message based on a point in timeacquired by the reception point acquisition unit and a delay timeacquired by the delay time acquisition unit for each of two receivedmessages.
 2. The in-vehicle communication system according to claim 1,wherein the calculation unit calculates, as the transmission cycle, atime difference between a point in time that goes back by a delay timefrom a reception point in time of a message received earlier and a pointin time that goes back by the delay time from a reception point in timeof a message received later.
 3. The in-vehicle communication systemaccording to claim 1, wherein the in-vehicle communication device on thereceiving side includes a periodic message determination unit thatdetermines whether the received message is a periodically transmittedmessage or an aperiodically transmitted message based on thetransmission cycle calculated by the calculation unit.
 4. The in-vehiclecommunication system according to claim 1, wherein the plurality ofin-vehicle communication devices include an in-vehicle communicationdevice that has the delay time measuring unit and the assigning unit andan in-vehicle communication device that does not have the delay timemeasuring unit and the assigning unit.
 5. The in-vehicle communicationsystem according to claim 4, wherein identification information foridentifying the message is added to the message, and the in-vehiclecommunication device on the receiving side includes an assignmentdetermination unit that determines whether or not a delay time isassigned to the message based on identification information added to thereceived message.
 6. An in-vehicle communication device that isconnected to a common communication line together with other in-vehiclecommunication devices and transmits and receives a message through thecommunication line, comprising: a reception unit that receives a messagewith a delay time from a point in time when transmission of a message tobe transmitted is first attempted to a point in time when thetransmission of the message is started; a reception point acquisitionunit that acquires a point in time when the reception unit receives themessage; a delay time acquisition unit that acquires a delay timeassigned to the received message; and a calculation unit that calculatesa transmission cycle of each message based on a point in time acquiredby the reception point acquisition unit and a delay time acquired by thedelay time acquisition unit for each of two received messages.
 7. Atransmission cycle calculation method for calculating a transmissioncycle of each message transmitted and received through a commoncommunication line by a plurality of in-vehicle communication devicesconnected to the common communication line, comprising: measuring adelay time from a point in time when transmission of a message to betransmitted is first attempted to a point in time when the transmissionof the message is started and assigning the measured delay time to themessage by an in-vehicle communication device on a transmitting side ofa message; and acquiring a point in time when a message from thein-vehicle communication device on the transmitting side is received,acquiring a delay time assigned to the received message, and calculatinga transmission cycle of each message based on a point in time and adelay time acquired for each of two received messages by an in-vehiclecommunication device on a receiving side of a message.
 8. The in-vehiclecommunication system according to claim 2, wherein the in-vehiclecommunication device on the receiving side includes a periodic messagedetermination unit that determines whether the received message is aperiodically transmitted message or an aperiodically transmitted messagebased on the transmission cycle calculated by the calculation unit. 9.The in-vehicle communication system according to claim 2, wherein theplurality of in-vehicle communication devices include an in-vehiclecommunication device that has the delay time measuring unit and theassigning unit and an in-vehicle communication device that does not havethe delay time measuring unit and the assigning unit.
 10. The in-vehiclecommunication system according to claim 3, wherein the plurality ofin-vehicle communication devices include an in-vehicle communicationdevice that has the delay time measuring unit and the assigning unit andan in-vehicle communication device that does not have the delay timemeasuring unit and the assigning unit.
 11. The in-vehicle communicationsystem according to claim 9, wherein the plurality of in-vehiclecommunication devices include an in-vehicle communication device thathas the delay time measuring unit and the assigning unit and anin-vehicle communication device that does not have the delay timemeasuring unit and the assigning unit.